Least Common Multiple (LCM)
Is the smallest positive integer that is evenly divisible by all the numbers.
We'll use this concept to answer the question.
We know the Red Line train has a schedule of 8 minutes, and the Blue Line train has a schedule of 10 minutes.
Both trains have just arrived at the station, so the next time they will coincide at the station is the LCM of 8 and 10:
To find the LCM, write 8 and 10 as the product of their prime multiples:
8 = 2*2*2
10 = 2*5
Now we take the factors the number of times they appear:
LCM = 2*2*2*5 = 40
Thus, both trains will arrive at the station at the same time in 40 minutes
Third choice: 40 minutes
